Visually checking for bias in housing price prediction

Suppose you're given the following data showing parcels that have been sold, the date they were sold, and the logerror between the estimate of the parcel's value vs. the actual sale price.

Using this data, provide a visualization of the logerror, and determine if the model used to predict parcel price seems to have a bias (either predicting too high or too low).
To help get you started, below is code (Python) to import the referenced dataset:

# Import libraries
%matplotlib inline
import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
# Import data
df = pd.read_csv('https://raw.githubusercontent.com/erood/interviewqs.com_code_snippets/master/Datasets/zillow_train_2017.csv')